Numerous tire pressure monitoring systems have been developed in order to detect when the air pressure within a tire drops below a threshold pressure value. A system typically includes a pressure switch, an internal power source, and a communications link. The pressure switch provides tire pressure information to a central receiver through the communications link. The communications link may be a wired or wireless link.
There has been an increasing need for tire pressure monitoring systems due to the use of "run flat" tires in vehicles. "Run flat" tires enable a driver to travel an extended distance after a substantial loss of air pressure within a vehicle tire.
Examples of tire pressure monitoring systems are disclosed in U.S. Pat. No. 5,285,189, U.S. Pat. No. 4,311,985, and U.S. Pat. No. 5,061,917.